Method of making diamond disks



Oct. 26, '1943. e. CROMPTON, JR,

thereof is a small metal ring 2|. through the ring 20 at one side near"the top and Patented Oct. 26,, 1943 UNITED METHOD OF MAKING DIAMONDDISKS George Crompton, Jr., Worcester, Mass., assignor to NortonCompany, Worcester, Mass., :1. corporation of Massachusetts ApplicationNovember 19, 1941, Serial No. 419,766 6 Claims. (01. 51-309) Theinvention relates to diamond abrasives and more particularly to a diskhaving a layer of diamond abrasive on one or both sides thereof.

One object of the invention is to provide an expeditious method formaking an article of the character indicated. Another object of theinvention is to provide a method for making a diamond coated metal diskwith the abrasive grains oriented normal to the face of the disk andevenly distributed thereon. Other objects will be in part obvious or inpart pointed out hereinafter.

The invention accordingly'consists in the features of construction,combinations of elements, arrangements of parts, and in the severalsteps and relation or order of each of said steps to one or more of theothers thereof. all as will be illustratively described herein, and thescope of the application of which will be indicated in the followingclaims.

In the accompanying drawing the single figure illustrates in sideelevation the plunger of a hydraulic press and in section certainmolding apparatus according to the invention.

I provide any suitable hydraulic press having a press plunger iii. A lowpressure press is adequate for purposes of the present invention. Ivulcanize or cement to the press plunger Iii a mold plate ll ofcomparatively hard vulcanized rubber which has a central hole i2. Thebottom surface i3 of this mold plate is coated with amalgam, for examplethe amalgam of tin with mercury which may be applied with a littlesodium silicate cement. For this purpose tin amalgam may be mixed with aminor portion of sodium silicate and water and then painted upon thebottom of the mold plate II.

The press has an upper cylinder portion 15 and a bottom press platen IS.The bottom press platen I6 is of course made of steel andthe pressitself constitutes a ground and in the case of the present invention theentire press should be well grounded to steam pipes of the factorybuilding or separately connected to an earth ground, such as a largemetal plate buried deep in the earth, by means of a substantial copperwire. I provide a steel bottom mold plate l8 having a central hole i9. Iprovide a mold ring 20 made out of Bakelite or the like, viz. moldedphenol formaldehyde resin, with a suitable dielectric iiller such asfinely divided quartz or asbestos. Molded into the ring 20 on the insideExtending internally threaded andreceives a binding post 23 on which arenuts 24 and rubber washers 25. A substantial copper, wire 26 leads to asource of direct current energy of the order of 1000 to 40,000 volts. Inthe central hole I! and in position to project into the hole I2 is aglass mold arbor l1.: Preferably the cylinder l5 of the press hasattachedthereto in any suitable manner a scale 30 and a pointer shouldbe attached to the press plunger Hi. It may consist of a short stem ofwood or metal 3i projecting from a rubber suction cup 32 which canreadily be placed in any desired position on the plunger l0.

Modern pressesare capable of accurate control and can be moved to ahairline position and held there for a few moments. By means of thescaleand pointer 3| the'position of the rubber mold plate II can beaccurately determined.

I first mold under light pressure a disk 35 from powdered metals. I mayuse any suitable mixture, for example that set forth in Edward Van derPyls Reissue Patent No. 21,165 reissued July 25, 1939, such as a mixtureof about 19% tin, the remaindercopper. Or I can use any one ofthemixtures set forth in Van der Pyls Patent No. 2,238,351 granted April15, 1941, for example 25% iron, 25% copper, 25% tin, 25% nickel byweight, as set forth therein. comparatively pure and finely. dividedmetal powders are used and such can'now be procured on the market foruse in powder metallurgy.

Simply by weighing out a predetermined quantity of metal powders andpressing in another press with standard mold equipment-I press the disk35 under slight pressure, for example to the order of 200 pounds to thesquare inch.- I may use the bottom mold plate iii, the Bakelite" ring 20and the glass arbor H in such other press and simply transfer thembodily to the position shown in the drawing herein after pressing off.the upper mold plate. Or I may proceed in any other suitable manner toestablish the conditions shown in the drawing herein. Before bringingdown the hydraulic press plunger 10 to the position shown, however, Isprinkle a weighed quantity of diamond abrasive grains 36 upon the uppersurface of the lightly pressed disk 35. I distribute them as well as Ican mechanically. I now bring the press plunger l0 down to the positionshown in the drawing.

At this moment I throw a main' remote control switch thatapplieselectromotive force of the order of for example 10,000 voltsthrough the in contact with t nt l '18 8 u h W h 5 wire 26 so that anelectric charge is distributed over the amalgam coated surface I3 of therubber mold plate II and as soon as the remote control switch is thrownI operate the hydraulic press lever to bring the press plunger Ill down.I then watch the indicator and apply a pressure of for example tons tothe square inch. As soon as the movement'of the mold plate I I haseliminated the air spacein the mold,.by a-manipulation of the remotecontrol switch I cut off the electrostatic charge.

The action is as follows: The moment the amalgam coated surface I3 wascharged with electricity via the electrostatic generator (not shown),main switch, wire 28, binding post 23, bushing 22 and ring 2|, thediamonds 36 were all picked up and moved to the lower surface I! of themold plate I I. were distributed evenly upon the surface II because ofthe charge that each one acquired and they were also oriented so as tostand with their longest dimension normal to the surface I3. Abrasivewill cling to a charged surface for a period of time of at least a fewseconds. Before the diamond particles 35 became fully charged (whichwould cause them to be repelled from the surface I3), the mold hadclosed and therefore they were embedded in the originally slightlycompacted but now more fully compacted disk 35. The result, afterraising the press plunger III and stripping the mold, is a pressed metaldisk 35 with a layer of diamonds 35 on one side nicely oriented andevenly distributed. It is clear that both sides of the disks can becoated withdiamonds by simplyrepositioning the disk in the mold andrepeating the process, but in such case the first pressing of thediamonds into the disk 35 should be at a lower pressure and a hardrubber liner should be used on top of the bottom plate I8 before thesecond pressing.

The hard rubber mold plate II is just, hard enough to press the diamondswellinto the disk 35 but also soft enough to eliminate shattering of thediamonds and to permit them to retain their orientation. As the amalgamwill inevitably wear off, the bottom surface I3 can be painted from timeto time therewith.

In order to prevent the Bakelite" ring 20 from going to pieces it may bereinforced with steel bands MI molded therein which will not, however,destroy its insulating properties. It should be understood, however,that the pressures given herein are representative merely and theapparatus dscribed is illustrative and an outer steel ring can be usedto reinforce the resin ring if desired,

After the article is made as described, it is taken to a sinteringfurnace and heated in a neutral or reducing atmosphere, preferablynitrogen, to a temperature of for example around 600 or 700 C. to sinterthe entire article. The result is a diamond abrasive disk with a singlelayer of diamonds on one or both sides Well embedded therein butnevertheless having their en s projecting therefrom providing a coolfreecuttlng wheel or disk.

Although the invention has been described specifically with reference tothe manufacture of diamond abrasive disks other abrasives such as emery.corundum, fused alumina, or silicon carbide could be used. Furthermore,if desired, a coating of metal plate may be applied around the diamondsafter the sintering operation more firmly to embed them. This may bedone by electroplating.

It will thus be seen that there has been pro- In so doing thediamondsvided by this invention an article and a method in which thevarious objects hereinabove set forth together with many thoroughlypractical advantages are successfully achieved. As marry possibleembodiments may be made of the above, invention and as many changesmight be made in the embodiment above set forth, it is to be understoodthat all matter hereinbefore set forth, or shown in the accompanyingdrawing, is to be interpreted as illustrative and not ina limitin sense.

I claim: Wu

1. Method of makingan article with a single layer coating. of abrasiveOrr thereof which comprises material into a body to a density whichpermits further substantial compacting and depositing abrasive grains ona surface of said body in evenly .spaced relation, and embedding theabrasive grains in said-body, including the'steps of depositing a layerof abrasive grains on a surface of said body electrically, energizingthe adjacent surface of another body substantially parallel to saidfirst body thereby imparting electrical charges to said abrasive grainsto cause them to assume an evenly and uniformly spaced relation whilethey move from the first body surface to the second body surface, andmoving the second body surface with substantial force against said firstbody surface thereby pressing said evenly and uniformly spaced abrasivegranules into the first body and simultaneously further compacting thesaid first body.

2. Method of making an article with a single layer coating of abrasiveon at least one side thereof which comprises compacting comminutedmaterial into a backing and distributing, evenly spacing, and embeddingabrasive granules in the preformed backing, including the steps ofdepositing the granules on one surface and, transferring them byelectricalattraction to a second surface by which they are returned tosaid first surface and seated therein.

3. The method of making an article with a single layer coating ofabrasive which comprises compacting comminuted material to form abacking, depositing abrasive granules on said backing, transferring saidgranules to another surface movable toward and away from said backingsimultaneously redistributing said granules in uniformly spaced relationto each other. and causing said other surface to move toward saidbacking so that the evenly and uniformly spaced granules are forced intoand seated in said backing.

4. The method of making an abrasive article which comprises pro-forminga backing of comminuted material, sprinkling a quantity of abrasivegrains upon the surface of said pre-formed backing, evenly spacing thesaid abrasive grains relative to one another by imparting electricalcharges to said grains and transferring them from said pre-formedbacking to an adjacent electrically energized surface, and causingrelative movement between said backing and adjacent surface to press theevenly distributed grains into said pre-formed backing.

5. The method of making an abrasive article which comprises the steps ofpre-forming a backing to act as a matrix for abrasive granules. firstsprinkling and mechanically distributing a quantity of diamond granules,which it is desired to embed in said matrix, upon'a surface andthereafter further distributing said granules for even spacing thereofin relation to one another H Zleast-ene side compacting comminuted bytransferring said granules to another surface and imparting electricalcharges to said granules during said transfer and thereafter bringingsaid backing and other surface together to embed said evenly distributedgranules in said backing.

6. The method of making an abrasive article which comprises pre-forminga backing and positioning it on one of two relatively movable andopposed press platens, distributing abrasive granules over the surfaceof said backing, between said platens, electrically energizing the otherof said press platens and thereby transferring the said granules to saidother press platen, and bringing said platen into contact with saidbacking to transfer the granules from said platen to said backing and toembed them in said backing,

GEORGE CROIVIPTON, JR.

